This section is intended to provide a background or context to the disclosed embodiments. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
Wireless communication systems are widely deployed to provide various types of communication content such as voice, data, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., bandwidth and transmit power). Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, 3GPP Long Term Evolution (LTE) systems, and orthogonal frequency division multiple access (OFDMA) systems.
Modem wireless communication systems use a variety of methods to determine that transmitted data is received correctly, and to provide for the retransmission of data when reception errors occur. For example, in 3GPP Long Term Evolution (LTE) Release 8 (Rel-8), a hybrid automatic repeat request (HARQ) methodology uses asynchronous automatic repeat request (ARQ) with soft combining, where erroneously decoded data packets are stored in a buffer memory and selectively combined with retransmitted data packets.
A HARQ process is a stop and wait construct. To allow for continuous transmission to a single mobile station (user equipment, or UE), multiple HARQ processes are operated in parallel. For each UE, there is one HARQ entity consisting of multiple HARQ processes. LTE Rel-8 specifies eight (8) HARQ processes in the downlink when operating in frequency division duplex (FDD) mode, with 8 different HARQ process numbers (HARQ IDs), based on an assumption about the round trip time between a base station (evolved Node B or eNode B) and a UE, including their respective processing times. When the operation is in time division duplex (TDD) mode, the number of HARQ processes in the downlink may vary between 4 and 15 depending on the downlink-uplink allocation schedule. In LTE Rel-8, each transport block (subframe) associated with a HARQ ID has a duration of 1 millisecond. Therefore, the time interval between the transmission of two transport blocks with the same HARQ ID cannot be less than 8 milliseconds in FDD mode.
If a UE receiver detects a reception error in a data block with a particular HARQ ID, and sends a repeat request (negative acknowledgement, or NACK) to the base station, the receiver expects to receive a data retransmission with the same HARQ ID no earlier than 8 ms after the original data block was received. Similarly, if the UE receiver decodes a data block without error and sends an acknowledgement (ACK) to the base station for the HARQ ID associated with the data, the receiver expects new data with the same HARQ ID no earlier than 8 ms after the first data block was received. However, there is a finite probability that a decoding error at the UE receiver can erroneously decode any transmission inside the 8 ms interval as a repeat of the particular HARQ ID. Existing LTE Rel-8 systems have no provision for handling such decoding anomalies and are subject to corruptions of the HARQ buffer or system crashes if the same HARQ ID is decoded twice in a time interval that is less than 8 ms. Additionally, there is no provision in LTE Rel-8 for negotiation between the base station and the UE to reduce the time interval if the UE has enhanced processing capability.